User blog comment:LegionZero/Nero's Parallels to Vergil and Sparda/@comment-967403-20140813075203/@comment-6769189-20140901075715

1) Yes it can be the only trigger, much like how a parent walking out can have long lasting adverse effect. for example, a girl with daddy issues. All the father has to do is leave her, and that can lead to all kinds of bad stuff to fill the void, like sleeping around. Now someone who, at the age of 8, took responsibility for the deaths of his only remaining family and held on to it since then, it's perfectly within reason that Evas death is the only reason he is the way he is.

2) Sparda had Yamato 2 thousand years ago. It has never been stated it was manifestation of Vergil's power. It existed as its own entity before him, they may be linked, but its not a symbol/representation of his power/essence. Rebellion however has been stated to be a manifestaion of Dante's power. It is a representation of his power/essence, and was presumably not in existence before Dante. You can even go as far to assume that Sparda created it himself from Dante's essence. There isnt any record of him weilding it, but it was at least in his possession at one point.